1. Field of the Invention
The present invention generally relates to a digital information system for processing digital contents information, particularly to a protection technique of digital contents information such as digital audio information.
2. Description of the Related Art
In general, digital contents information such as video and music is recorded in media such as a digital video disc (DVD) and compact disc (CD), and distributed via the media. Moreover, in recent years, networks such as the Internet and digital broadcasting have generally been utilized to distribute digital contents information.
Additionally, the digital information can easily be copied, modified, or processed by a personal computer or a digital audio and video (AV) apparatus. As a modification processing, for example, a method of ripping contents (usually a PCM file) as music piece data from a music CD by a software tool called a ripper is known. The PCM file taken from the music CD by the ripping can be converted to an MP3 file by a digital compression method, for example, in MP3 (MPEG-1/2 Audio Layer III) standard. Since the MP3 file is compressed at a high compression ratio, the file is easily distributed via the Internet. Moreover, it is easy to store the file in a disk drive built in the personal computer, CD-R (writable CD) as one of exchangeable media, and the like
From the background, since music contents (digital musical piece data) as digital audio information is distributed in large amounts via a CD for music, a protection function (i.e., copyright protection function) for preventing illegal copying is necessary.
As a method for realizing the protection function, a method of inserting a digital watermark (hereinafter referred to as WM information) in the music contents, constituted of a specific digital signal or digital pattern, and utilizing the WM information, is effective.
In the method of utilizing the WM information, for example, WM information indicating a copyright, and WM information indicating the number of copies are inserted beforehand in the music contents (PCM file) recorded in the CD. The personal computer or the digital AV apparatus detects the WM information from the music contents (PCM file) ripped from the music CD, and executes software for verifying validity. For example, the WM information indicates that the information can be copied. In this case, the personal computer or the digital AV apparatus checks that the ripping is valid within a limited range of the number of copies. Moreover, for example, the WM information can also indicate that copying is disabled. Then, the personal computer or the digital AV apparatus checks that ripping is invalid.
However, a verification method utilizing the WM information includes detection of the WM information and verification processing for music piece data, when all contents information recorded in the CD are, for example, music contents. Therefore, the personal computer or the digital AV apparatus is highly burdened by the verification processing, particularly, the detection processing of the WM information. This is one of the factors that reduces the use efficiency of a system resource.